Work rolls play an important role in the manufacture of metal and metal alloy sheet. For example, the aluminum industry places a high value on running aluminum alloy sheet lines in a continuous manner. Significant losses (energy, capacity, productivity, product damage, etc.) are associated with down time in aluminum alloy sheet production. High line speeds and forces, exerted by work rolls to reduce sheet gauge and improve sheet quality, cause significant wear of the work roll surface. Aluminum alloy sheets are used to form containers, such as can stock, vehicle components, corrosion resistant building materials, foil, and the like.
In a typical aluminum alloy sheet process, a slab can be cast and annealed (homogenized), and then, the aluminum alloy can be hot and cold rolled (reduction) to provide an intermediate gauge sheet. The slab and sheet temperatures and other operating controls can be critical in these steps. Thereafter, the aluminum alloy sheet can be passed through work rolls to adjust the thickness (final gauge) and improve the sheet surface finish.
In general, the work rolls that come in contact with aluminum alloy sheet desirably satisfy the following conditions: the rolls are wear resistant (extend the time between maintenance shut-downs); the rolls impart minimal surface damage to the aluminum alloy sheet; the rolls resist corrosion caused by different types of lubricant; and the life cycle cost of the rolls is low.
Common work rolls are fabricated from iron base alloys and have limited life caused by wear from high speed lines and high forces exerted by the rolling process. A roll is removed from service once its surface degrades and the roll negatively impacts the quality of the sheet. Examples of potential quality issues include banding, debris, vibration, surface defects (pits), increased surface roughness, and the like. Iron-based rolls can be chromium plated at an additional cost, but the roll life extension is limited.
There continues to be a need in the art for work rolls that can be used for extended periods of time without damaging the surface quality of the metal or metal alloy sheet. There also continues to be a need for work rolls that have improved resistance to wear and corrosion.